Such a surge shunt or lightning arrestor is designed to be connected to electrical equipment for the purpose of enabling it to be bypassed by pulses of surge current. Such surge current pulses occur, for example, during strokes of lightning. When this takes place, the lightning arrestor diverts the current pulse to ground, thereby protecting the electrical equipment and the circuit from being damaged or even destroyed.
In present lightning arrestors, the envelope surrounding the conductive electrical components, generally cylindrical varistor blocks, is constituted by a resin-impregnated winding of glass fibers, with the assembly being received in an insulating housing of an elastomer polymer that is weatherproof.
For a lightning arrestor to operate properly, intimate contact must be maintained between the varistor blocks. This contact is ensured by the structure of the envelope which puts the varistor blocks into axial compression. Where appropriate, a spring can be interposed between one of the end fittings and the varistor block situated at the corresponding end of the stack in order to achieve such axial compression.
Such lightning arrestors can fail, in which case they can be the seat of large leakage currents giving rise to high gas pressures inside the envelope and thus leading to the lightning arrestor bursting. To limit or prevent this risk of bursting, it is known to provide a glass fiber winding that leaves lateral openings so that gases can escape to the atmosphere. Such a structure, known from European patent No. 0 335 480, is nevertheless relatively expensive to manufacture and an object of the invention is to propose a shunt that is less expensive.